Volume stabilizer arrangement employing a photo-sensitive resistance element



July 11. 1967 w. R. AIKEN 3,331,012

VOLUME STABILIZER ARRANGEMENT EMPLOYING A PHOTO-SENSITIVE RESISTANCEELEMENT Filed Jan. 11,.1965

INPUT VOUTPUT INVENTOR WILLIAM ROSS AIKEN By M United States PatentOfifice 3,331,012 Patented July 11, 1967 3 331,012 VOLUME STABILIZERARRANGEMENT EM- PLOYING A PHOTO-SENSITIVE RESIST- ANCE ELEMENT WilliamR. Aiken, 10410 Magdalena Ave., Los Altos Hills, Calif. 94022 Filed Jan.11, 1965, Ser. No. 424,774 4 Claims. (Cl. 323-21) voltage passed throughthe circuit. The changes in the degree of illumination produced in thismanner change the resistance of the photosensitive element of thecircuit in such a manner as to maintain the output voltage of thecircuit stable.

' -The problem with arrangements of this type is that the response ofthe source of light to changes in the voltage of the signal passedthrough the circuit and the response of the photosensitive element tochanges in the illumination is often too slow depending upon the qualityand cost of the lamps and photosensitive resistor elements, and as aresult thereof the level of the output voltage of such circuits may riseinitially to a noticeable extent beyond the desired level whenever thesize of the input voltage incr'eases,.,and thereafter maydroptemporarily below the .desired level and may become scarcely audibledue to overcompensation, before it supplies a steady output voltage ofthe desired magnitude.

Another difiiculty with voltage stabilizer circuit arrangements of thetype here under discussion is that their release time is too short,i.e., they release control of the output signal too promptly wheneverthe signal drops below the desired level, Hence, when such arrangementsare used in the transmission of human speech, for example, they mayrelease control of the output signal during the dips between the peaksin the volume of the human voice. As a result thereof, the peaks in thevolume of the speech are reduced while the dips between the peaks areleft substantially unchanged, and the reproduced speech, therefore,becomes a monotonous slur that has lost all character and may even bedifficult to understand.

The initial attack time of voltage stabilizer arrangements employinginexpensive lamps and inexpensive photosensitive resistors can beshortened by using an initial increase in the volume of the outputsignal beyond the desired level as a control means to overvoltage thelamp which governs the resistance of the photosensitive resistanceelement. In this manner the increase in brightness of illumination ofthe lamp and the rate of reduction of the resistance value of thephotosensitive resistance element may be accelerated to such an extentthat the initial increase in the volume of the output signal is only ofthe briefest duration and scarcely noticeable, and there will be nonoticeable over-attenuation of the volume of the output signal.

To prevent immediate release in the control of the output signalwhenever the signal drops briefly below the desired level, such asduring the dips in the volume of the human speech, the line along whichthe control signal is applied to the element that .governs the currentflow in the power circuit of the lamp may be provided with a temporarymemory, such as a storage condenser. Said memory is charged by thecontrol signal, and upon disappearance of the control signal, itreleases slowly and extends the time of application of the controlcurrent at the control element in the power circuit of the lamp.

In systems of the type wherein an initial rise in the output volumebeyond the desired level occurs, the presence of a memory connected toprovide a predetermined release time presents a problem. It charges tothe level of the initial surge of the control voltage and when saidsurge disappears, the memory maintains the control element in the powercircuit of the lamp at the level of said surge for a longer period thannecessary to raise the illumination of the lamp rapidly to the requiredlevel. Hence, the lamp becomes brighter than necessary and staysbrighter for a longer time than required. As a result thereof the volumeof the output signal is reduced to a lower level than desired and, inthe case of human speech, may temporarily become inaudible.

It is an object of the present invention to provide a voltage stabilizerarrangement of the type described, which though constructed frominexpensive and therefore slowly responding components, becomes almostinstantaneously effective, yet does not overcompensate.

Another object of my invention is to provide a voltage stabilizerarrangement of the type referred to, that limits the output level of anapplied signal, such as the human voice, without destroying itscharacter.

In accordance with the invention the memory is provided with means whichdelay activation of the memory ,as the control current is applied to thecurrent flow control element in the power circuit of the source oflight. In this manner any surge of the control current can be fullyapplied to the control element in the power circuit of the lamp, and anadequate control current may be maintained on said element for the timenecessary to prevent premature release of the volume control mechanism,without causing overcompensation in the volume of the output signal. Thedelay means prevents the memory from being charged to the voltage levelof undesirable control current surges. Therefore, when the memoryreleases upon disappearance of the control current surge, it delivers anappropriately lower control voltage to the control element in the powercircuit of the lamp. This control voltage provides the desired delay inrelease time and yet maintains the lamp at only the brightness requiredto limit the volume of the output signal to the desired level.

The invention will be better understood by reference to the accompanyingdrawing which shows a circuit diagram of a preferred embodiment thereof.

The stabilizer arrangement of my invention illustrated in the drawingcomprises a variable volume changer of the type employing aphoto-sensitive resistor element. Said volume changer is a variableattenuator 10 formed by a fixed resistor 12 connected into the inputline 14 for the arangement and a photosensitive resistor element 16,such as a solid state photocell, connected in series with resistor 12between the input line and ground. The voltage developed across thephotosensitive element 16 is taken off at the junction point 18 ofresistors 12 and 16 and appears as the output signal in the output line2t) of the arrangement. The size of the voltage appearing in the outputline depends upon the relative values of the two series-connectedresistors 12 and 16. It will be large when the value of the resistorelement 16 is large compared with that of resistor 12, or small when thevalue of resistor element 16 is small as compared with that of resistor12. To vary the resistance value of the photosensitive resistor element16, said element is exposed to illumination from an adjacentlypositioned source of light such as the incandescent lamp 22, in such amanner that the resistance value of said photo-sensitive resistorelement is inversely proportional to the degree of illumination of thelamp. To stabilize the voltage output of volume changer irrespective ofvariations in the volume of the input signal, the degree of illuminationof the lamp is controlled by the signal that passes through the volumechanger such that the lamp burns brighter and therefore reduces theresistance value of the photosensitive resistance element 'when thesignal delivered to the volume changer increases in volume; and viceversa, the lamp dims when the signal applied to the volume changerbecomes weaker, which causes the value of the photosensitive resistorelement to increase and the output voltage developed across saidresistor element to increase correspondingly.

V In the embodiment of the invention illustrated in the accompanyingdrawing the power circuit of the lamp 22 includes a normallynon-conductive transistor 24 with its emitter and collector electrodesconnected into said circuit. The emitter to collector conductivity ofsaid transistor may be regulated by application of a control voltage toits base. The transistor 24 is by-passed by a rheostat 26 which is setto effect such energization of the lamp when the transistor 24 isnon-conductive (or in a predetermined state of conductivity) as willplace it on the threshold of illumination. Hence, when the transistor24- is rendered conductive or its conductivity is increased, the flow ofcurrent in the power circuit of the lamp increases and the lamp lightsup immediately.

To control the conductivity of transistor 24 a portion of the output ofvolume changer 10 is tapped off along a line 28, a measured part thereofdetermined by adjustment of a potentiometer 30 is rectified in a powerrectifier represented by the transistor 32 and the DC. voltage suppliedby the emitter of said transistor is applied along a control line 33 ascontrol signal to the base of transistor 24 across a grounded resistor34. To avoid premature disappearance of the control current supplied bythe emitter of transistor 32 a memory in the form of a relatively largecapacitor 36 is connected between the control line 33 and ground.

A delay bias may be placed upon the emitter of the rectifier transistor32 so that the emitter of the transistor will not supply a controlcurrent until the signal voltage applied to its base exceeds apredetermined level. As a result thereof the stabilizer arrangement ofthe invention does not respond to changes in the level of the outputsignal below a predetermined level, but any rise in the volume of theoutput signal beyond said limit causes the emitter of the transistor tosupply an exaggerated control current. For instance, the arrangement maybe such that a 10% increase in the level of the output signal mayproduce a 100% increase in the control current supplied by the emitterof transistor 32. In the particular embodiment of the inventionillustrated in the accompanying drawing, the transistor 32 is in itselfconstructed to perform in this manner. When an exaggerated controlcurrent of the described magnitude is applied to the base of thetransistor 24 in the power circuit of the lamp, a greatly amplifiedcurrent'is passed through the lamp and causes the lamp to gain rapidlyin brightness. This produces an immediate response of the stabilizerarrangement, that reduces the volume of the output signal. However, ifthe response of the stabilizer arrangement is not quick enough and anovershoot in the volume of the output signal occurs, the presence of thestorage condenser 36 between the control line 33 and ground introducesthe danger of holding the surge in D0. voltage at the base of transistor24 for a longer period than necessary for the lamp to reach the degreeof brightness required for proper attenuation, and the lamp may becometoo bright and/ or may retain its excessive brightness for too long sothat the volume of the output signal is excessively attenuated.

In the embodiment of the invention illustrated in the accompanyingdrawing a delay means in the form of a resistor 40 of relatively smallvalue is interposed between the control line 33 and the memory condenser36. Said resistor has the effect of delaying the charging of the storagecondenser and therefore prevents said condenser from charging to thefull value of the surge of control signal produced as a result of thebrief overshoot in the diitput volume of volume changer 10. Hence, whenthe condenser 40 discharges, it temporarily maintains a somewhat lowervoltage at the base of transistor 24 than the surge of control current.In this manner continued excessive illumination of the lamp andmomentary limitation of the output volume of the volume changer tolevels below the desired level will not occur. The presence of resistor40 between control line 33 and memory condenser 36 has the added effectof preventing said condenser from introducing any undesirable delay inthe application of control signal surges to the base of transistor 24.

As explained above, an initial overshoot in the output volume of thevolume changer may be used to apply an overly strong control signal ofbrief duration to the base of the transistor 24, to shorten the attacktime of the stabilizer arrangement. The presence of the memory condenser36 provides a predetermined release time which is sufficient to avoidconversion of the stabilized signal into a monotonous slur: and thepresence of the delay resistor 40 between the control line 33 and thememory condenser 36 prevents any noticeable overcompensation in thevolume of the output signal in spite of the presence of said storagecondenser.

Recapitulating the performance of the stabilizer a1- rangement of myinvention: when a signal applied to the input side of the stabilizerarrangement increases suddenly in volume as indicated at 42, the signal44 appearing in the output line 20 of the arrangement will likewiseincrease and may briefly over shoot the desiredvolume level as indicatedby the peak 45. The rise in the volume of the output signal above thedesired level causes the emitter of the rectifier transistor 32 tosupply a sudden surge of control current represented by the initial peak46 of the graph indicated at 48. This sudden surge of the controlcurrent is applied direcly to the base of the control transistor 24 inthe power circuit of the lamp and causes the flow of current in saidpower circuit to increase rapidly as indicated by the (negative) peak 50in the graph 52 causing the brightness of the lamp to increase rapidly.The surge of control current will also charge the memory condenser 36,but due to the presence of the resistor 40, the charging will occur moregradually and the charge will not reach the magnitude of the initialcontrol current surge as indicated by the graph 54 associated with thememory condenser 36. After the volume of the output signal has droppedto its desired level as indicated at 44, the initial surge of thecontrol current supplied by the emitter of rectifier transistor 32disappears before the lamp has reached an excessive degree ofbrightness. At this moment the condenser 36 discharges and maintains asomewhat lower and gradually decreasing control voltage at the base ofthe transistor 24 as indicated by the second part of graph 48. Thisdecreasing control voltage maintains the flow of current in the powercircuit of the lamp for a predetermined time at the level required tohol the volume of the output signal within the desired limits andprevents premature release of the control exercised upon the receivedsignal by the stabilizer arrangement of my invention.

In a practical embodiment of the invention as represented by theaccompanying drawing the components of the stabilizer arrangement wereas follows:

Resistor 12 ohms 50K Resistor 16 CL703CL Rheostat 26 ohms 250P-otentiometer 30 do 100K Resistor '34 do K Resistor 40 do 100 Capacitor36 microfarads 250 Lamp 22 No. 48 Transistor 24 2N1304 Transistor 322N1304 Under certain conditions it is desirable to place a resistor of3.3K ohms into the control line 33 as indicated at 56 in the drawing.

While I have explained my invention with the aid of a preferredembodiment thereof, it will be understood that the invention is notlimited to the specific circuit components shown and described by way ofexample, which may be departed from without departing from the scope andspirit of the invention.

I claim:

1. A voltage stabilizer arrangement comprising a volume changer havingan output line and including a variable resistance element and means forvarying the resistance value of said element including a power circuithaving a current flow control element therein adjustable by theapplication of control voltages thereto, circuit means connected betweensaid output line and said current flow control element for applying upona rise in the volume of the output of said volume changer in said outputline thereof a first control voltage to said current flow controlelement in a manner effective to depress the volume of the output ofsaid volume changer, and means for holding a second control voltage oflesser size at said current flow control element for a predeterminedduration upon decline of said first control voltage.

2. A voltage stabilizer arrangement comprising a volume changer havingan output line and including a photosensitive resistance element, meansfor illuminating said element to vary the resistance value thereof, apower circuit for said illuminating means including a current flowcontrol element adjustable by the application of control voltagesthereto, circuit means connected between said output line and saidcurrent flow control element for applying, upon a rise in the volume ofthe output of said volume changer in said output line thereof a firstcontrol voltage to said current flow control element to vary thebrightness of said illuminating means and hence the resistance value ofsaid resistance element in a manner effective to depress the volume ofthe output of said volume changer, and means for holding a secondcontrol voltage of lesser size at said curent flow control means for apredetermined duration upon decline of said first control voltage.

3. A voltage stabilizer arrangement according to claim 2 wherein saidmeans for holding a second control voltage of lesser size for apredetermined duration at said current flow control means is a delayresistor and a memory capacitor connected in series to said circuitmeans.

4. A voltage stabilizer arrangement according to claim 2 including meansfor holding said current flow control element in a condition whereinsaid lamp is at the threshold of illumination.

References Cited UNITED STATES PATENTS 2,353,218 7/1944 Burnham et a1.250205 X 3,171,032 2/1965 Holt 250-205 X 3,200,329 8/1965 Haisty 32321 XJOHN F. COUCH, Primary Examiner. A. D. PELLINEN, Assistant Examiner.

1. A VOLTAGE STABILIZER ARRANGEMENT COMPRISING A VOLUME CHANGER HAVINGAN OUTPUT LINE AND INCLUDING A VARIABLE RESISTANCE ELEMENT AND MEANS FORVARYING THE RESISTANCE VALUE OF SAID ELEMENT INCLUDING A POWER CIRCUITHAVING A CURRENT FLOW CONTROL ELEMENT THEREIN ADJUSTABLE BY THEAPPLICATION OF CONTROL VOLTAGES THERETO, CIRCUIT MEANS CONNECTED BETWEENSAID OUTPUT LINE AND SAID CURRENT FLOW CONTROL ELEMENT FOR APPLYING UPONA RISE IN THE VOLUME OF THE OUTPUT OF SAID VOLUME CHANGER IN SAID OUTPUTLINE THEREOF A FIRST CONTROL VOLTAGE TO SAID CURRENT FLOW CONTROLELEMENT IN A MANNER EFFECTIVE TO DEPRESS THE VOLUME OF THE OUTPUT OFSAID VOLUME CHANGER, AND MEANS FOR HOLDING A SECOND CONTROL VOLTAGE OFLESSER SIZE AT SAID CURRENT FLOW CONTROL ELEMENT FOR A PREDETERMINEDDURATION UPON DECLINE OF SAID FIRST CONTROL VOLTAGE.